1. Field of the Invention
The present invention relates to a resolver, which detects a rotational angle of a target object; an electric motor having the resolver; a power steering apparatus having the motor; and a method of manufacturing the resolver.
2. Description of the Related Art
Generally, a hydraulic power steering apparatus is used as a means for assisting steering of a vehicle. The hydraulic power steering assists manipulation of a steering wheel using hydraulic pressure generated from a pump which is actuated by an engine output. Recently, an electric power steering apparatus (hereinafter, referred to as an “EPS”) is used to assist handling of a steering wheel of a vehicle in such a way as to rotate a motor using a battery installed in the vehicle. The EPS is gaining popularity, because it is a more efficient system which reduces a power loss of an engine, compared to the hydraulic power steering apparatus which generates hydraulic pressure using the output of the engine.
In order to achieve a high accuracy control system, the EPS requires an angle detector which accurately detects a rotational angle of the motor. Meanwhile, vehicles are required to be accurately operated over a long period of time under various conditions. Therefore, the angle detector for the EPS which is one of components of a vehicle must also have high reliability. To achieve the above purpose, a variable reluctance type resolver which has a high detecting accuracy and which has high durability, compared to an optical encoder or a magnetic encoder, is used as the angle detector for the EPS.
In such a resolver, excitation coils and output coils of a stator unit are formed on teeth by winding wires around the teeth using a winder. Here, to enhance the detection accuracy of the resolver, the excitation coils and the output coils must be accurately formed. For this, promotion of high performance of the winder may be considered. However, in this case, the cost of manufacturing the winder is increased, and there is a technical limitation in enhancing the accuracy in winding the wires.